The invention relates to a roll bending device for the control of profile and flatness in the rolling of materials. In particular the invention relates to the well known principle of roll bending by using hydraulically actuated pistons to modify the load distribution between rolls of a rolling mill stand and a rolled material for example a metal plate or a strip in order to control the profile and flatness of the metal plate or strip. It is well known to apply bending to the work rolls of a rolling mill stand which might have an additional pair of backup rolls (4-high rolling mill stand) or additional pairs of backup and intermediate rolls (6-high rolling mill stand).
Furthermore the invention relates to a rolling mill stand with at least a pair of rolls pivoted in roll chocks and arranged in a mill stand housing and with at least one hydraulically actuated piston arranged in a bending block, for the bending of rolls, in order to allow control of profile and flatness in the rolling of metal strips or plates.
Typically, in systems known from prior art, hydraulic cylinders between work roll chocks, for the bearing of rolls in a rolling mill stand, are used to bend the work rolls in order to modify the profile and flatness of the rolled material.
In older prior art roll bending systems the hydraulic cylinders for the roll bending are built into either the work roll or the backup roll chocks. However, modern roll bending systems often use roll bending cylinders which are built into blocks, called roll bending blocks, which are attached to the mill stand housing. This type of system is preferred because the hydraulic connections can be permanently installed, they are generally capable of higher bending forces, and they are easier to maintain.
In addition to roll bending, many modern mills are equipped with roll shifting systems in which the work rolls can be axially shifted. By using work rolls with special profiles the axial shifting of the work rolls can be used to provide additional profile and flatness control capabilities.
In order to work with roll shifting, many modern roll bending systems are designed to work with the axial shifting of the work rolls. There are two main types of system in use. They are both designed to ensure that the roll bending force is applied to the centreline of the work roll bearing whatever the axial shift position of the roll might be. In one type the whole bending block containing the hydraulic cylinders is shifted axially together with the work rolls. In the other type the force is applied by a pair of bending cylinders and the distribution of load between the two cylinders is adjusted to keep the resultant total force centred on the bearing.
A fundamental problem with known roll bending block systems is the fact that especially with thick rolled material the top work roll chock loses the capability of support against side loads.
Some systems known from prior art also provide support where the work roll chock wing contacts the mill stand housing but this is not satisfactory due to the small area of contact. High stresses at the work roll chock wing and the difficulty of providing both good support for the chock and allowing enough clearance for axial shift of the rolls and for roll change are the disadvantages of this systems. As the side loads on the work roll chocks are high this problem is an important consideration for mills rolling thick material such as plate mills.
According to the known prior art, it is very difficult to achieve good support of the work roll chock when rolling thick material with existing bending block designs. Consequently many modern plate mills still use the older in-chock type of bending systems in order to be able to handle thick material.